1. Field of the Invention
The present invention relates to an integrated circuit package, and more particularly, to an integrated circuit package with a heat spreader to dissipate heat.
2. Description of Related Art
Because the integrated circuit semiconductor device is getting more complicated in function and smaller in size, the flip chip semiconductor device is seeing more wide-spread use, since flip chip mounting permits a high component density and fast accessing time. FIG. 4 shows a conventional integrated circuit package which is of a well known "flip chip on board" type packaging. By welding the solder bumps 42 of a die 40 to a printed circuit board 41, the die 40 is electrically connected to the printed circuit board 41. An underfill 43 is injected between the die 40 and the printed circuit board 41 to securely consolidate the die 40 with the printed circuit board 41 so that the solder joints between the die 40 and the printed circuit board 41 will not be damaged due to different degrees of thermal expansion of the die 40 and the printed circuit board 41 upon thermal excursions, which the integrated circuit semiconductor device experiences during operation.
However, due to the fact that the aforementioned flip chip semiconductor device is of small volume and with high power density, the thermal resistance greatly increases. The major heat dissipation paths are from the backside of the die 40 to the environment and from the lower portion of the die 40 to the printed circuit board 41. Unfortunately, the underfill filled between the die 40 and the printed circuit board 41 is of an insulating material, such as epoxy resin, whose heat conducting capability is extremely low. Therefore, the heat from the die 40 is difficult to be conducted to the printed circuit board 41 and the heat dissipation capability of such a flip chip semiconductor device is unsatisfactory.
In order to eliminate the aforementioned heat dissipating problem, an additional heat cap or heat spreader may be employed to assist in dissipating heat. FIG. 5 shows a flip chip integrated circuit package having a die 50 attached to a substrate 53 that is mounted on a printed circuit board 54. A metal heat sink 51 is further mounted on the top of the die 50 via adhesive 52 such that the heat from the die 50 is dissipated to the heat sink 51. With such a flip chip packaging structure, the effective heat dissipating area can be increased by using the heat sink 51. However, the heat sink 51 is secured to the die 50 by adhesive 52, thus the load on the die 50 is heavy so that the connection between the die 50 and the substrate 53 is likely to be damaged due to stress generated by the heavy load. Therefore, the reliability of such a packaged semiconductor device is difficult to promote.
Alternatively, FIG. 6 shows a flip chip integrated circuit package, which has a metal heat cap 61 disposed on a substrate 63 to cover a die 60. The heat cap 61 is adhered to the substrate 63 through epoxy resin 62. A heat conductive adhesive 64 is filled between the heat cap 61 and the die 60. Thus, the heat from the die 60 can be dissipated out through the heat cap 61. With such a packaging structure, the heat cap 61 is adhered to the substrate 63 through the epoxy resin 62 that is unable to transfer heat. Thus, the heat can not be effectively conducted to the substrate 63 to be dissipated. Moreover, the aforementioned heat sink 51 and the heat cap 61 are with large footprints with respect to that of the die 50, 60. However, since the density of the electronic package is getting higher and the size of electronic product is getting smaller, adding such large heat dissipation elements to the flip chip device is obviously undesired, as it will greatly increase the space required by the flip chip device. Thus, there is a need for the above integrated circuit packages to be improved.
Among the known patents related to the heat dissipation of a flip chip integrated circuit package, U.S. Pat. No. 5,847,929 granted to Bernier et al. has disclosed the use of an adhesive of silicone or flexible-epoxy to attach a heat sink to a semiconductor chip. U.S. Pat. No. 5,726,079 granted to Johnson has provided a thermally conductive planar member in packaging a flip chip. U.S. Pat. No. 5,650,662 granted to Edwards et al. has disclosed a heat spreader that is directly bonded to an electronic device package. U.S. Pat. No. 5,856,911 granted to Riley has provided an integrated circuit package having a top die attach area and a bottom heat spreader thermally coupled to the die. The above patents are provided to dissipate heat out of integrated circuit packages with only one heat dissipation path which us from the die upward to the environment. Therefore, they can not be used to effectively solve the aforementioned heat dissipation problems.